One type of electrosurgical procedure is endoscopic urological surgery using a resectoscope. Such systems are well known in the art, examples being given in U.S. Pat. Nos. 5,007,907 and 6,322,494. Such systems include an electrosurgical instrument deployable by means of a resectoscope, and an electrosurgical generator powering the instrument. Instruments used in electrosurgical urology surgery are either bipolar, in which case two electrodes are present at the distal end of the instrument, or monopolar, in which case one electrode is present on the instrument and a second electrode is provided in the form of a patient return plate.
Bipolar urological surgery is generally carried out as an “underwater” procedure, with the electrodes immersed in a conductive fluid such as normal saline. Monopolar urological surgery is also carried out with the active electrode immersed in a fluid, but in this case the fluid is generally a non-conducting fluid such as glycine. In monopolar surgery the return electrode is a remote patient plate attached to the patient at an area away from the surgical site.
In either arrangement, fluid is introduced to the surgical site and extracted therefrom, usually using irrigation and suction passages within the resectoscope. However, the effective circulation of fluid within the surgical site is difficult to achieve, and fluid adjacent the electrode or electrodes can become elevated in temperature. If the temperature of the fluid rises locally to excessive levels, unwanted tissue damage can occur. To avoid this, the flow rate of the fluid circulating through the surgical site can be increased. However, while this may be sufficient to reduce the temperature of the fluid adjacent the electrode or electrodes, too high a fluid flow can prevent the electrode or electrodes from functioning correctly. For example, an electrode may be incapable of “firing up” and vaporising tissue if the fluid is flowing past the electrode too quickly for an area of plasma to form around the electrode.